Yes, you can over carb your beer. The simplest way to carb a beer and have the carbonation level come out perfect every time is to hook the keg up to the proper pressure gas, and wait three weeks. Here is a good program to help with setting your regulator.
Don't remember who posted this method but this is how I do it and it works well:
1. Hook up gas and set to serving pressure, do not hook up liquid line
2. Allow gas to fill keg, when you hear it stop disconnect
3. Roll keg on floor for several minutes to absorb gas
4. Reconnect gas and repeat
5. Do this procedure 3-5 times
6. Hook up gas final time and leave alone
7. Allow 2-3 days to absorb and settle and then hook up liquid and serve
I find this works well with no ability over carbonate because you are force carbing at serving psi. I have not had an over carbonated keg yet.